1. Field of the Invention
The invention is directed to a single mode optical waveguide fiber for use in telecommunication systems and more particularly, a waveguide fiber which has a large effective area to reduce non-linear effects, and combine bend resistance, low attenuation, low dispersion, and low dispersion slope.
2. Technical Background
Optical amplifier technology and dense wavelength division multiplexing (DWDM) techniques are typically required in numerous telecommunication systems, such as those systems that require high power transmissions for long distances, as well as in metropolitan area networks.
With respect to high power transmissions for long distances, the definition of high power and long distances is meaningful only in the context of a particular telecommunication system wherein a bit rate, a bit error rate, a multiplexing scheme, and perhaps optical amplifiers are specified. There are additional factors, known to those skilled in the art, which have impact upon the meaning of high power and long distance. However, for most purposes, high power is an optical power greater than about 10 mW. In some applications, single power levels of 1 mW or less are still sensitive to non-linear effects, so that the effective area is still an important consideration in such lower power systems. A long distance is one in which the distance between electronic regenerators can be in excess of 100 km. The regenerators are to be distinguished from repeaters which make use of optical amplifiers. Repeater spacing, especially in high data density systems, can be less than half the regenerator spacing. To provide a suitable waveguide for a multiplex transmission, the total dispersion should be low, but not zero, and have a low slope over the window of operating wavelength.
Generally, an optical waveguide fiber having a large effective area, Aeff, reduces non-linear optical effects, including self phase modulation, four wave mixing, cross phase modulation, and non-linear scattering processes, all of which can cause degradation of signals in high powered systems. A waveguide fiber having a segmented core can generally provide a large effective area while limiting the non-linear optical effects.
The mathematical description of these non-linear effects includes the ratio, P/Aeff where P is the optical power. For example, a non-linear optical effect can be described by an equation containing a term, exp [Pxc3x97Leff/Aeff], where Leff is effective length. Thus, an increase in Aeff produces a decrease in the non-linear contribution to the degradation of a light signal. A core having multiple segments each characterized by a refractive index profile, a relative index, and a radius, meets many of the desired functional properties.
The requirement in the telecommunication industry for greater information capacity over long distances, without electronic signal regeneration, has led to a reevaluation of single mode fiber index profile design. The focus of this reevaluation has been to provide optical waveguides which:
reduce non-linear effects such as those noted above;
are optimized for the lower attenuation operating wavelength range around 1550 nm;
are compatible with optical amplifiers; and,
retain the desirable properties of waveguides such as high strength, fatigue resistance, and bending resistance.
A suitable waveguide fiber must have low linear dispersion and low attenuation as well. In addition, the waveguide fiber must display these properties over a particular extended wavelength range in order to accommodate wavelength division multiplexing used for multiple channel transmission.
As noted above, dense wavelength-division multiplexing technology is used within metropolitan area networks to meet the increasing demand for bandwidth to allow more channels to operate within a single fiber, as well as to allow the transfer of single transmissions requiring significant amounts of bandwidth, such as multimedia files and applications. DWDM technology requires new fiber designs with low finite dispersion across the entire WDM window to improve system performance and reduce system costs.
Standard-single mode fibers currently in use in metropolitan area networks typically exhibit a dispersion of near 17 ps/nm-km in the 1550 nm operating window. Therefore, dispersion compensation is needed for a WDM system having a bit rate of 2.5 Gb/s or higher. Dispersion compensation increases system cost and can result in an attenuation penalty. It would be desirable to design an optical fiber that exhibits a lower dispersion than that currently available in both the 1300 nm and 1550 nm operating windows.
Waveguide designs which also are relatively easy to manufacture and which permit management of dispersion are favored, because of their low cost and added flexibility. The designs described herein are well suited to a dispersion managing strategy in which the waveguide dispersion is varied along the waveguide fiber length to toggle the total dispersion between positive and negative values.
U.S. Pat. No. 5,781,684 incorporated herein by reference as though fully set forth in its entirety, discloses and describes segmented core waveguide fibers having large effective areas. A feature of the segmented core of the waveguide fiber disclosed in the ""684 patent is that at least one of the segments has a negative or a relative refractive index. The present application discloses and describes segmented core waveguide fibers that provide a unique set of functional properties.
This invention meets the need for a single mode optical waveguide fiber that offers the benefits of a relatively large effective area together with a substantially flat dispersion slope over an extended operating range.
The invention relates to a single mode optical waveguide fiber including a segmented core. Each of the segments is described by a refractive index profile, a relative refractive index percent, and an inner and outer radius. The optical waveguide fiber further includes a clad layer surrounding and in contact with the core, and having a refractive index profile.
In a preferred embodiment, the index profiles are further selected to provide a dispersion slope of less than about 0.07 ps/nm2-km. A further embodiment has a dispersion slope of equal to or less than about 0.057 ps/nm2-km while maintaining a bending induced loss on the pin array test of less than about 6 dB and preferably less than 0.68 dB.
In addition, embodiments having induced attenuation loss due to lateral load bending less than 0.25 dB/m and preferably less than 0.208 dB/m are disclosed and described.